Drilling apparatuses using pressurized medium have been know for a long time in the mineral industry, and they comprise: a drilling device, such as a down-the-hole drill or the like, the first end thereof having a drilling means, such as a drill bit, or the like, and the second end of the preferably connectable with one or several drill rods for increasing the drilling depth of the drilling device. The drilling device is at least partially arranged to be driven by a to-and-fro or corresponding percussion movement and comprises at least percussion means for generating the percussion movement driven by a pressurized liquid medium supplied through a first flow channel, Such drilling apparatus further preferably include scavenging means for removing drilling waste generated by the effect of the drilling means, the scavenging means supplying a scavenging agent through a second flow channel preferably in connection with the drilling means of the drilling device, and a support frame being at least indirectly supported by the ground.
Apparatuses of the type described above, using pressurized air, have been widely used in mineral industry for a long time. It is an advantage of a drilling device which is to be placed down the hole that the percussion impact is directed to the drill bit, whereby the energy losses and unnecessary wearing of the components of the apparatus can be reduced in comparison with solutions having the drilling device placed at the rear end of drilling rods. Conventionally in drilling devices driven by pressurized air, pressurized air is used also for scavenging the crushed aggregate. However, it is not advantageous to drive a drilling device by pressurized air, because answer other thing this requires a compressor unit with a very high capacity. Furthermore, the efficiency of a pneumatic system is clearly lower than that of a hydraulic system.
The use of a hydraulic drilling machine is known, for example from the published international application PCT/EP89/00256. In the solution of the above application, the driving unit of the drill rod, driven by a pressurized medium, conveys a to-and-fro rotational motion to the drill rod, as distinguished from the rotational motion conventionally used. Thus, hoses are arranged between the drill rod and the walls of the drill hole, and upon inserting or removing rods, hoses are fed into the hole or reeled in from the hole. To achieve an optimal drilling efficiency and save the hoses, the angle of rotation of the drill rod is preferably limited to the range of 180.degree.-360.degree.. For minimize the wearing of the hoses, an embodiment is presented in the publication where the drill rod comprises two outwardly open longitudinal channels in which the hoses are inserted for feeding in and out the pressurized oil of the drilling machine to be placed in the hole. The hydraulic hoses are o thus preferably inside the circle of the drill rod. Scavenging air is preferably delivered through a hollow drill rod.
The solution described in the above-mentioned publication is not very practical, because massive machinery is required for the handling of hoses. Both hoses must be provided with reeling rolls and driving units, their need of space being determined by the depth of the hole to be drilled. It is difficult to handle the hoses in the drilling situation, and careless installation may result in environmental damage in case of damage to the hoses. Also, hoses of different lengths must be used or they must be fitted with joints when holes of different lengths are drilled, which results in further environmental risks.